1. Field of the Invention
The present invention relates to an image forming apparatus, such as a coping machine, a printer, a scanner, a facsimile machine, and a multifunction peripheral furnished with some of the capabilities of these machines, and to a method for erasing image data to erase image data related to a specific job, such as a print job, from a memory device provided to the image forming apparatus to save the image data after the job is completed.
2. Description of the Related Art
In a case where a copy of a certain document is made using a multifunction peripheral (MFP) as a copying machine, the document is first read by the scanner. Image data of the document is thus obtained. The image data is saved in the hard disc drive (HDD) provided as a memory device. The image data is then read out from the HDD and restored to an image again, and this image is printed on a sheet of paper. Even when a print job is suspended by a trouble, such as paper jamming, the configuration as above enables printing to be resumed using the image data saved in the HDD and thereby eliminates the need to scan the document again after the trouble is removed. In addition, a print job, such as sorting, multiple printing, and double face printing, can be executed smoothly. When the print job ends, the image data saved in the HDD is erased so that the document will no longer be reproduced.
A print job by the printer, a print job of reception data by a facsimile machine, and a data transmission job by a facsimile machine can be executed in the same manner. For example, for a print job that uses the MFP as a printer, print data written in a page description language is first transmitted to the MFP from a personal computer or the like. The print data is then subjected to bit map conversion page by page by a raster image processor (RIP) provided to the MFP. Page data is thus generated. The page data is temporarily saved in the HDD. The page data is then read out from the HDD and restored to an image, and this image is printed on a sheet of paper. After the print job ends, the page data saved in the HDD is erased so that the page data will no longer be reproduced.
Generally, the HDD includes a data save region and a file management region. In an HDD provided to the image forming apparatus, image data (or page data) is saved in the data save region. Also, information (so-called FAT (File Allocation Table) information) to know at which address in the data save region the image data is saved is stored in the file management region.
One method for erasing image data saved in the HDD is a method for erasing the FAT information related to the image data from the file management region. According to this data erasing method, the image data itself is not erased from the data save region. However, once the FAT information is erased, the location at which the corresponding image data is present becomes unknown, which inhibits an access to the image data. Accordingly, the image data is assumed to have been erased.
This data erasing method has an advantage that loads on the processor that performs operation control of the image forming apparatus and data processing can be reduced. According to this data erasing method, however, it is not impossible to reproduce image data because the image data itself is not erased. Should an evil-minded third party obtain an HDD in which highly confidential documents or the like are saved in the form of image data, there is a risk that the documents are restored.
Given these circumstances, as another data erasing method, there is a method for erasing image data by writing random data over the image data saved in the HDD several times. According to this method, however, it takes a long time to erase data. Also, the performance is deteriorated because, for example, a new job is limited while the data is being erased. Further, there is a problem that the life of the HDD is shortened as the number of accesses to the HDD increases.